1. Field of the Invention
The present invention relates to a computer system and a method for controlling the frequency of command execution.
2. Description of the Related Art
For example, companies and the like manage data using storage controllers that have relatively large storage capacities for handling large amounts of various types of data. The storage controller, for example, comprises large numbers of storage devices, such as hard disk devices. The storage controller can provide RAID (Redundant Array of Inexpensive Disks)-based storage areas to a host computer (hereinafter, host). A logical volume is created by making use of the storage areas of storage devices. The host issues a read command or a write command by specifying a desired logical volume. Consequently, the host either reads out data from the desired logical volume or writes data to the desired logical volume.
The storage controller comprises a plurality of logical volumes, and can execute a different process for each logical volume. Therefore, for example, while copying data from a first logical volume to a second logical volume, the storage controller is able to simultaneously write write-data received from the host to a third logical volume.
Thus, there is the danger that the processing of a command issued from the host will be delayed due to the other processing being executed inside the storage controller, thereby lowering response performance. Although not directly related to this problem, as one known prior art, there is a system that classifies a plurality of communication ports of the storage controller as priority ports and non-priority ports, and processes a command that arrives at a priority port on a priority basis (JP-A-2002-108567).
In the above-mentioned prior art, a command received via a priority port is processed on a priority basis, thereby making it possible to improve response performance to the host that is using the priority port. However, the prior art is for carrying out I/O (Input/Output) control between the host and the storage controller, and is not for carrying out I/O control inside the storage controller or between storage controllers.
Therefore, since processing is either executed inside the storage controller or between a plurality of storage controllers, the processing of a command issued by the host may be delayed, and the response performance of the storage controller may be lowered.